1. Field of the Invention
The present invention relates to an image forming apparatus utilizing electron beams.
2. Related Background Art
In an image forming apparatus including a cathode ray tube (CRT), further size enlargement has been demanded and researches have intensively been performed. Moreover, with the size enlargement, the thinning, lightening and cost reduction of the apparatus have become an important problem. However, since the CRT deflects the electrons accelerated with a high voltage with a deflecting electrode, and excites phosphors on a face plate, in principle, a depth is necessary for the size enlargement, and it is difficult to provide a thin and light apparatus. As the image forming apparatus which can solve the above-described problem, the inventors have researched a surface conduction electron emitting device, and an image display using the surface conduction electron emitting device.
The inventors have attempted applying a multi-electron beam source by an electric wiring method, for example, as shown in FIG. 11. Specifically, a multiplicity of surface conduction electron emitting devices are two-dimensionally arranged, and these devices are wired in a simple matrix form as shown in FIG. 11 to form the multi-electron beam source.
In FIG. 11, numeral 4001 schematically denotes the surface conduction electron emitting device, 4002 denotes a row direction wiring, and 4003 denotes a column direction wiring. Additionally, for convenience of the drawing, a 6×6 matrix is shown, but the scale of the matrix is not limited to this, and a sufficient number of devices for performing a desired image display are arranged and wired.
FIG. 12 shows the structure of the image forming apparatus using the multi-electron beam source, and the structure includes a rear plate 4005 provided with a multi-electron beam source 4001, an outer frame 4007, a face plate 4006 provided with a fluorescent layer 4008, and a conductive member (metal back) 4009. Moreover, a high voltage of several kilovolts to several tens of kilovolts is applied to the conductive member (metal back) 4009 disposed on the face plate 4006 via a high-voltage introduction terminal 4011 from a high-voltage power source 4010.
In order to output desired electron beams in the multi-electron beam source in which the surface conduction electron emitting devices are wired in the simple matrix, appropriate electric signals are applied to the row direction wiring 4002 and the column direction wiring 4003. For example, to drive one arbitrary row of surface conduction electron emitting devices in the matrix, a selection voltage Vs is applied to the row direction wiring 4002 of the selected row, and additionally a non-selection voltage Vns is applied to the row direction wiring 4002 of a non-selected row. In synchronization with this, a drive voltage Ve is applied to the column direction wiring 4003 to output the electron beams. According to this method, a voltage Ve-Vs is applied to the surface conduction electron emitting devices of the selected row, and a voltage Ve-Vns is applied to the surface conduction electron emitting devices of the non-selected row. When Ve, Vs, Vns are set to voltages with appropriate magnitudes, the electron beams with desired intensities are outputted only from the surface conduction electron emitting devices of the selected row. Moreover, when different drive voltages Ve are applied to the column direction wirings, the electron beams with different intensities are outputted from the devices of the selected row. Moreover, since the response rate of the surface conduction electron emitting device is high, by changing a time length for applying the drive voltage Ve, the time length for outputting the electron beams can also be changed.
The electron beams outputted from the multi-electron beam source 4001 by applying the voltage as described above are radiated to the conductive member (metal back) 4009 to which a high voltage Va is applied, so that the fluorescent layer (image forming member) 4008 as a target is excited to emit light. Therefore, for example, by appropriately applying a voltage signal in accordance with image information, an image display is constituted.
The image forming apparatus applies the high voltage Va to the conductive member (metal back) 4009, produces an electric field between the rear plate 4005 and the face plate 4006 to accelerate the electrons, and excites the fluorescent material to emit light so that an image is formed.
Here, to realize the thinning of the image forming apparatus, the thickness of the image forming apparatus needs to be reduced, and for this purpose a distance between the rear plate 4005 and the face plate 4006 has to be reduced. Since the interval between the rear plate 4005 and the face plate 4006 is set to about several millimeters, a high electric field of 1 kV/mm or more is produced between the rear plate 4005 and the face plate 4006.
The conductive member (metal back) 4009 has a purpose of applying the high voltage Va to the entire fluorescent layer, preventing the fluorescent material from being charged, and extracting the light emitted rearward (rear plate direction) from the fluorescent material toward the front by a mirror surface effect. Therefore, the conductive member (metal back) is preferably a continuous film. Moreover, the metal back 4009 needs to be a very thin film because the accelerated electrons have to be passed through the metal back 4009 to excite the fluorescent material. However, since the fluorescent material is usually a powder, the fluorescent film becomes porous, and considerable surface irregularities are present.
Moreover, particularly when the fluorescent materials of three primary colors (red, blue, green) are disposed as the fluorescent film, a black interval defining member (black matrix or black stripe) is usually disposed between the color fluorescent materials in order to prevent a mixed color between the color fluorescent materials, defines the interval between the color fluorescent materials, prevents a color deviation from occurring even when the electron beam position slightly deviates, and absorbs external light and enhances the image contrast, as well as for other reasons. The considerable irregularities are also present on the surface of the interval defining member.
For the above-described reasons, a filming process is usually performed before the conductive member (metal back) is prepared, because the continuous film cannot be formed by directly forming the film of the conductive member (metal back) 4009.
The filming process comprises preparing an acrylic resin film on the surface of the fluorescent layer, and flattening the surface of the fluorescent layer. Subsequently, by forming a film of conductive member on the flattened film by a vacuum deposition process or the like, the conductive member (metal back) can be prepared as the continuous film. Moreover, after the conductive member (metal back) is prepared, the resin film is calcined and removed by thermal decomposition.